A float; esp. a floating object moored to the bottom, to mark a channel or to point out the position of something beneath the water, as an anchor, shoal, rock, etc.

Anchor buoy, a buoy attached to, or marking the position of, an anchor. -- Bell buoy, a large buoy on which a bell is mounted, to be rung by the motion of the waves. -- Breeches buoy. See under Breeches. -- Cable buoy, an empty cask employed to buoy up the cable in rocky anchorage. -- Can buoy, a hollow buoy made of sheet or boiler iron, usually conical or pear-shaped. -- Life buoy, a float intended to support persons who have fallen into the water, until a boat can be dispatched to save them. -- Nut ∨ Nun buoy, a buoy large in the middle, and tapering nearly to a point at each end. -- To stream the buoy, to let the anchor buoy fall by the ship's side into the water, before letting go the anchor. -- Whistling buoy, a buoy fitted with a whistle that is blown by the action of the waves.